It was a grimoire. Not just some podunk D&D spellbook, but a limited-edition "Grimoire of Marisa." How could I pass that up? Turns out, very easily. Well, at least I didn't cosplay as one of the actual characters; I don't have the legs for a dress.
What does a human do when he finds himself in a mystical land where all basic tenets of common sense and natural laws take a vacation? Why, create a survival guide for the next hapless sod that finds themself in the plotbuckery that is Equestria!